October Monthly update Patch KB5127648 installed on systems, after installed and restart the system, system network not working, In Network Properties showing unidentified network. Please help to resolve this issue.

Vishal Jadhav 40

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Answer accepted by question author

Daphne Huynh (WICLOUD CORPORATION) 2,540 Microsoft External Staff Moderator

Welcome to Microsoft Q&A!

Thank you for reaching out and for providing the details about the issue.

Based on the timing and the symptoms you described, this behavior may be related to an authentication security change introduced with KB5127648, rather than necessarily indicating a failure of the physical network adapter.

With this update, Windows strengthens NTLMv1 security by changing the default behavior of BlockNtlmv1SSO from Audit mode (0) to Enforce mode (1) when the registry value has not already been configured. In Enforce mode, Windows blocks the generation of NTLMv1-derived credentials for Single Sign-On (SSO).

This change applies to devices where Credential Guard is disabled and the BlockNtlmv1SSO registry value is not configured, and it may affect Wi-Fi, Ethernet, or VPN connections that rely on MS-CHAPv2-based authentication. Therefore, the timing of the network issue after installing KB5127648 makes this an important possibility to validate. However, the "Unidentified network" status alone is not sufficient to confirm that this authentication change is the cause.

1. Temporary workaround

If your affected network uses MS-CHAPv2-based authentication, you can temporarily return BlockNtlmv1SSO to Audit mode for validation.

Open Command Prompt as Administrator and run:

reg add "HKLM\SYSTEM\CurrentControlSet\Control\Lsa\MSV1_0" /v BlockNtlmv1SSO /t REG_DWORD /d 0 /f

After applying the change, disconnect and reconnect the affected network connection and check whether the network is identified correctly and connectivity is restored.

Please consider this a temporary compatibility workaround, rather than a permanent solution.

The security update should remain installed. If this workaround restores connectivity, it would indicate that the network authentication configuration should be reviewed so that the environment does not continue to depend on NTLMv1-derived credentials.

2. Next validation step

After making the change, please verify whether:

The "Unidentified network" status disappears.
The affected Ethernet or Wi-Fi connection is identified normally.
Network access is restored.

If connectivity returns after changing BlockNtlmv1SSO to 0, this provides a much clearer direction for your network or identity administrators to review the authentication method used by the affected network.

If the issue continues even after this validation, I sincerely understand that you may want us to investigate further here. However, this is where Microsoft Q&A has an important support limitation.

Microsoft Q&A is a public community troubleshooting forum rather than an environment-specific support channel. Contributors can provide guidance based on the symptoms and Microsoft documentation, but I do not have access to your organization's affected computers, network infrastructure, authentication configuration, policies, or the diagnostic data required to determine why a particular production network is failing.

For example, determining the exact cause beyond this documented KB5127648 behavior may require reviewing configuration and diagnostic information from the affected environment. Those details cannot be remotely collected or investigated through a Q&A thread.

Therefore, if changing BlockNtlmv1SSO to 0 does not restore connectivity, I would recommend opening a Microsoft Support request rather than continuing with additional speculative troubleshooting in the forum. A support engineer can work with your organization through the appropriate support channel and perform the environment-specific investigation that cannot be performed through Microsoft Q&A.

This recommendation is not intended to redirect you without assistance. It is to make sure the issue reaches a support channel that can investigate the affected environment appropriately, particularly because the problem is affecting network connectivity following a security update.

Reference:

October 13, 2026—KB5127648 (OS Builds 26300.9711, 26200.9711 and 26100.9711) | Microsoft Support

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AI answer

KB5127648 can interrupt Wi‑Fi, Ethernet, or VPN authentication when the connection uses MS-CHAPv2, Credential Guard is disabled, and BlockNtlmv1SSO is absent; verify that condition first, then temporarily switch affected devices to Audit mode while migrating the network authentication method.^1^

Verify whether the documented authentication change applies

This applies to Windows 11 24H2/25H2/26H2 and certain enterprise Wi‑Fi, wired 802.1X, or VPN connections using MS-CHAPv2, including PEAP-MSCHAPv2 and EAP-MSCHAPv2. It does not establish that every “Unidentified network” after this update has the same cause.^2^

Open Event Viewer.
Go to Applications and Services Logs > Microsoft > Windows > NTLM > Operational.
Reproduce the connection failure and look for Event ID 4025 at that time.
- 4025 means NTLMv1-derived single sign-on credentials were blocked.
- 4024 means that dependency was detected but allowed under Audit mode.
Check the current setting from an elevated Command Prompt:

reg query "HKLM\SYSTEM\CurrentControlSet\Control\Lsa\MSV1_0" ^
 /v BlockNtlmv1SSO

If the value is missing, KB5127648 uses Enforce mode internally on eligible devices. If there is no Event 4025, or this is a basic home network that does not use MS-CHAPv2/802.1X, skip to If Event 4025 is absent.

Temporary mitigation for confirmed Event 4025 failures

Run this from an elevated Command Prompt on a small test group first:

reg add "HKLM\SYSTEM\CurrentControlSet\Control\Lsa\MSV1_0" ^
 /v BlockNtlmv1SSO /t REG_DWORD /d 0 /f

A restart is not required. Disconnect and reconnect the affected Ethernet, Wi‑Fi, or VPN connection. Alternatively, manually entering credentials can continue to work in Enforce mode.^2^

Security warning: Audit mode reduces the protection supplied by Enforce mode. Treat it as a scoped, temporary exception—not a permanent fleet-wide fix.

The permanent resolution is to identify and replace the MS-CHAPv2/NTLMv1-derived single sign-on dependency in the RADIUS, 802.1X, or VPN configuration. After remediation, return the device to Enforce mode:

reg add "HKLM\SYSTEM\CurrentControlSet\Control\Lsa\MSV1_0" ^
 /v BlockNtlmv1SSO /t REG_DWORD /d 1 /f

If Event 4025 is absent

Collect evidence before resetting adapters or deleting profiles, because those actions can remove useful diagnostics.^3^

For Wi‑Fi, run these from an elevated Command Prompt:

ipconfig /all
route print
netsh wlan show drivers
netsh wlan show interfaces
netsh wlan show profiles
netsh wlan show wlanreport

Then check:

Whether ipconfig /all shows a valid DHCP address, default gateway, and DNS servers. An address beginning with 169.254 indicates that DHCP configuration was not obtained.
The HTML report path returned by netsh wlan show wlanreport.
Event Viewer > Applications and Services Logs > Microsoft > Windows > WLAN-AutoConfig > Operational.
The adapter model, driver version, and date against the computer or adapter manufacturer’s supported driver. Microsoft specifically recommends comparing driver and firmware versions when connectivity starts after an update.^3^

Compare an affected system with an unaffected system on the same VLAN or SSID. This distinguishes a client authentication or driver problem from DHCP, switch-port, VLAN, or RADIUS infrastructure failure.

Controlled rollback test

If several systems failed immediately after KB5127648, Event 4025 is absent, and no DHCP/driver cause is identified, uninstall the update from one test device:

Start > Settings > Windows Update > Update history.
Under Related settings, select Uninstall updates.
Select KB5127648 and choose Uninstall.
Restart and test the same connection.

Some updates cannot be uninstalled. Removing a security update also removes its security fixes, so use this only to confirm causality and keep deployment paused rather than broadly removing it.^4^

If rollback restores networking but Event 4025 was absent, retain the affected/unaffected logs, adapter driver details, Windows build, authentication type, and failure timestamp for a Microsoft Support case.

References

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1 additional answer

Vishal Jadhav 40 Reputation points

2026-10-26T09:16:27.19+00:00

After uninstalled October-2026 Month update Patch (rollback) system network working ok.
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Vishal Jadhav 40 Reputation points

2026-10-29T04:38:00.32+00:00

reg add "HKLM\SYSTEM\CurrentControlSet\Control\Lsa\MSV1_0" ^ /v BlockNtlmv1SSO /t REG_DWORD /d 0 /f

reg add "HKLM\SYSTEM\CurrentControlSet\Control\Lsa\MSV1_0" ^ /v BlockNtlmv1SSO /t REG_DWORD /d 1 /f

reg add "HKLM\SYSTEM\CurrentControlSet\Control\Lsa\MSV1_0" ^ /v BlockNtlmv1SSO /t REG_DWORD /d 1 /f Whether ipconfig /all shows a valid DHCP address, default gateway, and DNS servers correct. Above setting done, but still showing Ethernet Authentication Failed. Please suggest further troubleshooting steps for resolve this issue.

Daphne Huynh (WICLOUD CORPORATION) 2,540 Reputation points Microsoft External Staff Moderator

2026-10-29T07:47:37.92+00:00

Thank you for testing the registry settings and sharing the additional results.

The “Ethernet Authentication Failed” message is an important clue. At this point, I would focus on the 802.1X authentication process rather than DHCP, the default gateway, or DNS configuration.

The October 2026 update KB5127648 changes the default behavior of BlockNtlmv1SSO from Audit to Enforce when the registry value was not previously configured and Credential Guard is disabled. In Enforce mode, Windows blocks NTLMv1-derived credentials used for Single Sign-On (SSO). This can affect Ethernet 802.1X connections that use MS-CHAPv2, including PEAP-MSCHAPv2 and EAP-MSCHAPv2.

The fact that connectivity returns after uninstalling KB5127648 further supports investigating this authentication path.

Based on the symptoms, the most likely cause is that the wired 802.1X profile is using PEAP/TEAP with MS-CHAPv2 and relies on an authentication flow affected by the NTLMv1 SSO hardening introduced with the October 2026 update.

However, since you have already tested BlockNtlmv1SSO=0 and the authentication still fails, I would not recommend making additional registry changes or repeatedly switching the value between 0 and 1. The next step should be to confirm which part of the authentication process is actually failing.

Recommended troubleshooting step

Please reinstall KB5127648 on one test computer only, reproduce the Ethernet authentication failure, and immediately check:

Event Viewer > Applications and Services Logs > Microsoft > Windows > NTLM > Operational

Check for an event generated at the same time as the Ethernet authentication failure:

Event ID 4025 indicates that an attempt to use NTLMv1-derived credentials for SSO was blocked by policy.

Event ID 4024 indicates that the use of NTLMv1-derived credentials was audited rather than blocked.

If BlockNtlmv1SSO=0 is being applied successfully, you would normally expect this dependency to be audited rather than blocked.

I also recommend asking your network administrator to correlate the same failure timestamp with the 802.1X RADIUS/NPS authentication logs. This is particularly important because “Ethernet Authentication Failed” indicates that the connection is failing during authentication, so the IP configuration is unlikely to be the primary issue at this stage.

Workaround and long-term direction

If the logs confirm that the wired network uses MS-CHAPv2 and depends on the affected legacy credential behavior, I would not recommend uninstalling or permanently deferring the security update as the solution.

The long-term remediation is to have the network or identity administrator migrate the affected 802.1X configuration away from MS-CHAPv2-based password authentication to a supported certificate-based authentication method such as EAP-TLS. This is a recommendation moving away from MS-CHAPv2 based connections in favor of certificate-based authentication, which is not affected by this SSO restriction.

BlockNtlmv1SSO=0 should therefore be considered only a temporary and scoped compatibility exception while the authentication environment is being remediated, because Audit mode provides less protection than Enforce mode.

Next validation step

The most useful result to collect now is the NTLM Operational event generated at the exact time of the Ethernet 802.1X authentication failure, together with the corresponding RADIUS/NPS rejection.

If Event ID 4025 is generated, this provides strong evidence that the connection depends on the NTLMv1-derived SSO behavior and gives your network team a clear direction to review the PEAP/TEAP and MS-CHAPv2 configuration.

If Event ID 4025 is not present, or the Ethernet connection still fails after BlockNtlmv1SSO=0 has been confirmed and Event ID 4024 is being generated, I would avoid making further registry changes based only on the symptoms. At that point, the failure would need to be investigated by correlating the EAP exchange, client 802.1X configuration, RADIUS/NPS rejection reason, domain authentication, and, if necessary, network traces.

I would also like to clarify the support limitations of Microsoft Q&A in this situation.

Microsoft Q&A is a public community troubleshooting forum. I can use the documented behavior of KB5127648 to help identify the likely authentication path and recommend appropriate validation steps, but I do not have access to your organization's Ethernet 802.1X profile, RADIUS/NPS configuration, certificates, authentication policies, domain environment or the diagnostic traces needed to determine the exact cause of an environment-specific authentication failure.

Therefore, if the issue remains after the validation above, I recommend opening a Microsoft Support request and providing the support engineer with the failed authentication timestamp, NTLM Operational events, corresponding RADIUS/NPS rejection event and reason code, Windows build, and the EAP method configured for the wired connection. This will allow the engineer to correlate the client-side and authentication-server diagnostics and investigate the exact failure in your environment.

I understand that you are looking for a definitive resolution, especially since uninstalling the October update restores connectivity. However, once the documented registry workaround has been tested without resolving the authentication failure, continuing to suggest registry changes through a public forum would become speculative. I would rather be transparent about that limitation and direct the remaining investigation to a support channel that can securely review the required logs and configuration from your environment.
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October Monthly update Patch KB5127648 installed on systems, after installed and restart the system, system network not working, In Network Properties showing unidentified network. Please help to resolve this issue.

Verify whether the documented authentication change applies

Temporary mitigation for confirmed Event 4025 failures

If Event 4025 is absent

Controlled rollback test

1 additional answer

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